Field
The invention relates to over-the-air testing of a device in an anechoic chamber.
Description of the Related Art
When a radio frequency signal is transmitted from a transmitter to a receiver, the signal propagates in a radio channel along one or more paths having different angles of arrivals, signal delays, polarizations and powers. Also a frequency may change due to the Doppler effect. These changes may cause variation in signal strength and fadings of different durations. In addition, noise and interference due to other transmitters interfere with the radio connection.
A transmitter and a receiver can be tested using a radio channel emulator emulating real circumstances. In a digital radio channel emulator, a radio channel is usually modelled with an FIR filter (Finite Impulse Response).
Communication between a DUT (Device Under Test) and a base station of a radio system can be tested using an OTA (Over-The-Air) test, where a real DUT, such a subscriber terminal, is surrounded by a plurality of antennas coupled with an emulator in a chamber which has as low echoes as possible. The emulator may be coupled to or act as a base station and emulate propagation paths between the subscriber terminal and the base station according to a channel model by generating independent Rayleigh faded signals, for example. OTA antennas transmit pre-processed communication signals to the DUT on the basis of weights determined by the emulated radio channel.
However, the OTA chamber has surfaces such as walls, cables and antenna stands which reflect the signals transmitted by the OTA antennas. Often the OTA antennas themselves cause echoes in the chamber. The unwanted reflections cause distortion to the emulated radio channel and deteriorate the quality of the emulation. On the other hand, it is technically very challenging to make the OTA chamber anechoic enough for the radio channel emulation, particularly with a moderate budget. Hence, there is need for a new approach to perform emulation in the OTA chamber.